The present invention relates generally to grouping and switching of spare circuits. Particularly, the present invention relates to varying the size and quantity of spare circuit groups in response to varying the number of active circuits.
In order to provide more products to their subscriber base, cable television companies are offering access to the Internet through their cable modem (CM) boxes. The benefits in using the cable companies instead of a dial-up Internet Service Provider is multiple services under one bill, always-on access, and, in some cases, higher speed access.
In order to provide their customer""s with Internet access, the cable companies use some of the 50-800 MHz spectrum typically set aside for their television channels to provide the bandwidth required for the data transfers. A typical cable system has the bandwidth to provide 100 television channels to its subscribers. Each NTSC television signal requires 6 MHz of bandwidth.
In order for a cable subscriber to access the Internet through their cable television provider, the subscriber must have a CM. The CM is similar to the Cable Modem Termination System (CMTS) equipment required at the cable company""s headquarters, except for the greater size required at the headquarters. This is to accommodate a greater number of signals than is required by the home modem.
The home CM box and the CMTS use well-known Ethernet frames to communicate between them. The cable system, however, uses a different modulation scheme, Quadrature Amplitude Modulation (QAM), than is normally used in an Ethernet scheme.
Using QAM, the downstream (from the cable company equipment to the home CM) data rate is in the range of 30-40 Mbps for each 6 MHz channel. This can typically accommodate between 500 and 2000 subscribers. The more subscribers that the cable company tries to fit in that spectrum, however, the lower the bandwidth that is provided to each subscriber.
The upstream data flow is different and more complex. In the past, cable companies did not have to worry about providing bandwidth for the customer to communicate in the upstream direction. Pay-per-view movies and sports events, however, required this ability. The cable companies, therefore, set aside the 5-42 MHz spectrum to allow the home CM to communicate in the upstream direction. The cable companies now use this 5-42 MHz spectrum to provide the necessary upstream access to the Internet from the home CM.
Cable companies, as well as other Internet Service Providers, are currently introducing Quality of Service (QoS) to Internet access. The current Internet routing model of xe2x80x9cbest effortxe2x80x9d service now provided to all users, packets, and traffic flows is being replaced with services that differentiate between packets.
FIG. 1 illustrates a typical prior art CMTS block diagram. The CMTS typically is comprised of a cable interface card (101) to provide the interface signals and modulation to the signals transmitted to the home modem. An Ethernet card (110) interfaces the CMTS to the Internet by providing appropriate timing, control, and data signal formats for the Internet. A buffer circuit (105) between the cable interface card (101) and Ethernet card (110) stores data in both the upstream and downstream directions when the processing in either the cable interface card or the Ethernet card is slower than the incoming data.
FIG. 2 illustrates a typical prior art circuit card layout of a CMTS. This CMTS is comprised of a number of cable interface cards (201-205) connected to a mid-plane (210). Each cable interface card (201-205) has an associated switch card (211-215). Each cable interface card is associated with a number of cable customers.
When one of the cable interface cards fails, those customers lose service until the failed card is manually swapped out for a good one. Additionally, the cable company may want to increase their capacity by reducing the reliability of the equipment. This would require being able to easily increase the number of cable interface circuit cards while decreasing the number of spare circuits without replacing the entire card cage structure. There is a resulting unforeseen need for a more reliable cable interface system to provide different size and quantity of spare/active circuit groups depending on the number of active circuits that need back-up circuits.
The present invention encompasses a system for providing variable spare circuit group sizes and variable quantities of spare circuit groups. This enables a cable company to change the number and ratio of spare circuit card and active circuit cards without changing the card cage structure. The system comprises a plurality of active circuits that provide information signals and at least one spare circuit that is substantially similar to each of the plurality of active circuits.
A plurality of switching circuits, each of which is coupled to a different active circuit of the plurality of active circuits, comprises a switch that is daisy-chain coupled with a switch from an immediately preceding and/or an immediately succeeding switching circuit. One feed-through switch circuit for each spare circuit is daisy-chain coupled to one of an immediately preceding and an immediately succeeding switching circuit or an immediately succeeding switching circuit.
A controller circuit is responsible for monitoring RF signals that are provided by the active circuits to each of the switching circuits. When an RF signal is absent or when an active circuit is found to be faulty through the use of real-time monitoring techniques, the controller circuit instructs the switch to change position such that the spare circuit replaces the failed active circuit.
The present invention provides the capability, by daisy-chaining the switches and the feed-through circuits, of making different size spare groups of spare circuits with active circuits as well as different numbers of spare groups. This is accomplished by replacing a feed-through circuit with a switching card circuit and the paired spare circuit with an active circuit.